"AN IMPROVED PROCESS FOR THE PREPARATION OF PRIMER FORMULATIONS USEFUL FOR THE PROTECTION OF METALLIC STRUCTURES AND COMPONENTS AGAINST CORROSION AND ABROSION."

Abstract

An improved process for the preparation of primer formulations useful for the protection of metallic structures and components against corrosion and abrasion which comprises of mixing of fly ash powder, 10 to 29 weight % of inorganic pigments , 1% by weight of anti settling agents, 18 to 22 weight% of resin such as Bisphenol-A epichlorohydrin epoxy resin and 23 to 27 weight % of organic solvent to obtain a smooth paste; grinding and dispersing the paste a primer base; mixing 5 parts by weight of primer base with 1 part by weight of polyamidoamines as a curing agent to obtain the primer formulation.

Full Text

The present invention relates to an improved process for the preparation of primer formulations useful for the protection of metallic structures and components against corrosion and abrasion.
The significance of the invention is the development of new primer formulations based on waste materials and with improved performance properties as compared to the similar formulations based on the conventional materials. The new fly ash based formulations offer improved resistance to corrosion in humidity and salt spray conditions. They possess excellent resistance to water, chemicals and organic solvents. The fly ash based formulations also exhibit better abrasion resistance. The improved properties of the formulations are contributed by fly ash, which as an extender is superior to many of the traditionally used mineral extenders like whiting, barytes, china clay etc. The properties of fly ash contributing to its superiority are its chemical inertness, abrasive nature, less oil absorption and low specific gravity values. The added advantage of fly ash as extender is due to no chemical upgradation required and simple processing unlike conventional mineral extenders which require crushing, grinding, levigation etc. to bring ores to the final forms. The developed formulations based on fly ash can be applied as industrial maintenance and marine coatings for protection on metallic structures and components in severe corrosive and abrasive environments.
Reference may be made to published paper by Y. Singh & S.M. Singh in Research and Indusrty, June 1971, 16, (2), 93-94 entitled 'Use of fly ash in emulsion paints' wherein preparation of water dispersible polyvinyl acetate (PVA) emulsion paints was carried out using fly ash for building applications. Three compositions of PVA emulsion paints were formulated with varying fly ash percentage. The formulations are as mentioned below
(Table Removed)

The drawbacks are inferior water resistance and other protective properties of the formulations as resistance to corrosion and abrasion on account of which they have limited applications.
Reference may be made to published paper by B.B. Gogte & Alok Agrawal in
Paintindia, Oct. 1994, XLIV, (10), 51-56 entitled 'Fly ash based coatings' wherein work
has been reported on preparation of water thinnable alkyd emulsion red oxide primers,
using fly ash. The formulation of primers are given below:
(Table Removed)

The drawbacks are inferior water and chemical resistance of the formulations. The presence of water in the formulations causes a greater tendency towards increasing corrosion of the substrate material. The addition of surfactants to reduce the higher surface tension of water further leads to the formation of films with poorer water resistance. Hence, they can not be applied where protection against severe corrosive and abrasive environments is required, as in industrial and marine atmospheres.
Reference may be made to USSR patent no. SU 883117, dt. 19811123, titled "Antiabrasive resin coating composition- containing specified polyepoxy resin binder, poly-amine hardener and power station fly ash", wherein 34-40 weight % of diglycidyl ether of furfural resorcinol as resin component, 8-8.3 weight % of alkoxylated polyamine as hardener, 6.7-7 weight % of organic solvent (1:1 mixture of acetone & toluene) and 45-51 weight % of coal ash has been used.
The drawbacks are inferior anticorrosive properties of the formulations for protection of metallic structures against corrosion.
The present invention describes the formulation of solvent borne primers incorporating fly ash as extender with improved anti corrosive and anti abrasive properties. The formulations can provide a better degree of protection in industrial and marine atmospheres. The influence of fly ash on performance properties of the primers have been studied.
The main object of the present invention is to provide an improved process for the preparation of primer formulations useful for the protection of metallic structures and components against corrosion and abrasion which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a process wherein fly ash, an industrial waste product, has been used.
Accordingly the present invention provides an improved process for the preparation of primer formulations useful for the protection of metallic structures and components against corrosion and abrasion which comprises: i) mixing by known methods 25 to 44 weight % of fly ash powder, 10 to 29 weight % of pigments, 1% by weight of antisettling agents, 18 to 22 weight % of resin such as Bisphenol-A epichlorohydrin epoxy resin and 23 to 27 weight % of organic solvent, to obtain a smooth paste having pigment volume concentration in the range of 48.51% to 58.69% ;
ii) grinding and dispersing the paste obtained in step (i) by known methods till the particle size is in the range of 6-7 microns to obtain a primer base ; iii) mixing 5 parts by weight of primer base obtained in step (ii) with 1 part by weight of curing agent ouch as modified polyamidoamines as a curingage
In an embodiment of the present invention the fly ash powder used may be of particle size
In another embodiment of the present invention, the pigments used may be such as zinc chromate, barium chromate, lead chromate, strontium chromate, red oxide of iron (mineral grade or chemically prepared) or mixtures thereof, having particle size
In yet another embodiment of the present invention the antisettling agent used may be such as fine silica, aluminium stearate or soya lecithin.
In still another embodiment of the present invention, the organic solvent used may be such as xylene, toluene, N- butyl alcohol or mixtures thereof.
The improved process of the present invention involves washing, drying and sieving of ESP (Electro Static Precipitator) fly ash and pigments to
epichlorohydrin epoxy with xylene and N-butyl alcohol as solvents. Modified polyamidoamine is added as curing agent to the prepared base. The preparation is done by mixing resin and solvent as per the formulation with other powdered ingredients to form mill base of paste consistency which is then fed in a ball mill with steel balls for grinding. The process of grinding accompanied by dispersion is continued till the desired particles size (6-7 microns) is obtained on Hegmans Guage. The viscosity and specific gravity are determined. The prepared formulations are applied on mild steel (m.s.) panels by brush in single coat for determination of film properties. Test for corrosion resistance is conducted by exposing m.s. samples painted on both surfaces and sides sealed with wax to 95% relative humidity and temperature cycle of 42-48 °C for seven days in a chamber as per the standards and also to a fine spray of 3% salt solution in a cabinet. The damage to the primer film, if any like blistering, chalking, checking, cracking etc. are visually observed. Immersion tests are conducted in distilled water, 5% Na2CO3, 2% H2SO4, 1% NaOH and organic solvents like toluene and mineral sprit. Visual observation are taken at regular intervals as in case of humidity and salt spray tests. High stress (two body) abrasion test is conducted using a standard abrasion tester. Samples are exposed to natural weathering at 45° facing south as per the standard practice.
Results indicate an improved performance of fly ash based formulations in both humidity as well as salt spray resistance tests over other formualtions based on conventional materials and commercial compositions. The improvement is attributed to the properties of fly ash which due to the presence of unreactive oxides of Si, Al, Fe etc acts as a barrier for the corrosive species to reach the surface of the substrate material. As also reported elsewhere, silica and alumina on account of their durability, are used to coat pigments to improve their durability characteristics. It is understood that fly ash does not chemically inhibit corrosion like phosphate and chromate inhibitors but delays corrosion by slowing down the diffusion of corrosive species to the substrate. The performance of fly ash based primers was good in acidic as well as basic solutions in immersion tests where as the formulations based on conventional materials were completely failed in acidic medium and showed poor results in basic solutions. The solvent resistance of fly ash primers was also good as no damage to the primer film was observed during immersion. The improved chemical and solvent resistance of fly ash

primers is obviously attributed to the chemical inertness of fly ash constituents. The other properties which make fly ash a useful extender are abrasion resistance, less absorption and low specific gravity. As indicated in the experimental results, fly ash has silica and alumina as major constituents which are abrasive in nature and therefore impart abrasivity to the ash. This property helps to enhance the abrasion resistance of primers in which fly ash is incorporated. Less oil absorption of fly ash indicates less resin demand without affecting other primer properties. The oil absorption of an extender depends on its physical structure i.e. particle size and shape. The microstructure of fly ash suggests its spherical structure with smooth outer surface and therefore a smaller surface area, responsible its low oil absorption. Hence, more amount of fly ash as compared to other mineral extenders can be incorporated and a reduction in the amount of resin required is achieved. The specific gravity of fly ash is 2.14, less as compared to other extenders which gives the advantages of using higher percentage of ash without any adverse increase in bulk density of the formulation. The film properties of fly ash primers like drying time, film thickness and brushability are good and in a desirable range. The properties obtained in solvent based formulations using fly ash are superior to those of water based primers as the presence of water in the formulation may initiate blistering and corrosion of the substrate and hence are not applicable where high degree of protection is desirable.
The following examples are given by way of illustration of the present invention and should not be contrued to limit the scope of the present invention.
EXAMPLE-I:
25 weight % of prewashed and dried fly ash sieved to particle size
giving proper time for curing, as 5-10 minutes, the primer is applied by brush or spraying.
EXAMPLE- 2
30 weight % of prewashed and dried fly ash sieved to particle size
EXAMPLE- 3
35 weight % of prewashed and dried fly ash sieved to particle size
EXAMPLE- 4
40 weight % of prewashed and dried fly ash sieved to particle size
55.04%. The paste is grinded and dispersed in a laboratory ball mill till the particle size is in the range of 6-7 microns to obtain a primer base. 5 parts by weight of the primer base is mixed with 1 part by weight of modified polyamidoamine curing agent. After giving proper time for curing, as 5-10 minutes, the primer is applied by brush or spraying.
EXAMPLE- 5
44 weight % of prewashed and dried fly ash sieved to particle size
The improved formulations of the primers as cited in the above examples, have excellent protection against corrosion and abrasion as compared to other water based formulations. They offer good drying time, film thickness, brushability and other mechanical film properties as scratch hardness and impact resistance. They do not undergo hard settling during storage as observed in many commercial samples. The primers can be applied by brush or spraying. The base and the curing agents are mixed just prior to application as per the proportions indicated in the above examples. The physical properties and film characteristics of the formulations have been mentioned below in table below:

We Claim:
1. An improved process for the preparation of primer formulations
useful for the protection of metallic structures and components
against corrosion and abrasion which comprises of:
i) mixing by known methods 25 to 44 weight % of fly ash powder, 10 to 29 weight % of inorganic pigments , 1% by weight of anti settling agents, 18 to 22 weight% of resin such as Bisphenol-A epichlorohydrin epoxy resin and 23 to 27 weight % of organic solvent to obtain a smooth paste having pigment volume concentration in the range of 48.51% to 58.69%;
ii) grinding and dispersing the paste obtained in step (i) by known methods till the particle size is in the range of 6-7 microns to obtain a primer base;
iii) mixing 5 parts by weight of primer base obtained in step (ii) with 1 part by weight of polyamidoamines as a curing agent.
2. An improved process as claimed in claim 1, wherein fly ash used
may be of particle size
3. An improved process as claimed in claims 1, wherein the pigments
used may be such as zinc chromate, barium chromate, lead
chromate, strontium chromate, red oxide of iron (mineral grade or
chemically prepared ) or mixtures thereof, having particle size
microns.
4. An improved process as claimed in claims 1, wherein the anti
settling agent is fine silica, aluminium stearate or Soya lecithin.
5. An improved process as claimed in claims 1, wherein the organic
solvents used are xylene, toluene, N-butyl alcohol or mixtures
thereof.

6, An improved process for the preparation of primer formulations useful for the protection of metallic structures and components against corrosion and abrasion substantially as herein described with reference to the examples.